EG2008

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https://diglib.eg.org/handle/10.2312/264

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Transparent and Specular Object Reconstruction
(The Eurographics Association, 2008) Ihrke, Ivo; Kutulakos, Kiriakos N.; Lensch, Hendrik P. A.; Magnor, Marcus; Heidrich, Wolfgang; Theoharis Theoharis and Philip Dutre
This state of the art report covers reconstruction methods for transparent and specular objects or phenomena. While the 3D acquisition of opaque surfaces with lambertian reflectance is a well-studied problem, transparent, refractive, specular and potentially dynamic scenes pose challenging problems for acquisition systems. This report reviews and categorizes the literature in this field. Despite tremendous interest in object digitization, the acquisition of digital models of transparent or specular objects is far from being a solved problem. On the other hand, real-world data is in high demand for applications such as object modeling, preservation of historic artifacts and as input to data driven modeling techniques. With this report we aim at providing a reference for and an introduction to the field of transparent and specular object reconstruction. We describe acquisition approaches for different classes of objects. Transparent objects/phenomena that do not change the straight ray geometry can be found foremost in natural phenomena. Refraction effects are usually small and can be considered negligible for these objects. Phenomena as diverse as fire, smoke, and interstellar nebulae can be modeled using a straight ray model of image formation. Refractive and specular surfaces on the other hand change the straight rays into usually piecewise linear ray paths, adding additional complexity to the reconstruction problem. Translucent objects exhibit significant sub-surface scattering effects rendering traditional acquisition approaches unstable. Different classes of techniques have been developed to deal with these problems and good reconstruction results can be achieved with current state-of-the-art techniques. However, the approaches are still specialized and targeted at very specific object classes. We classify the existing literature and hope to provide an entry point to this exiting field.
Interactive Tools for Scientific and Medical Illustration Composition
(The Eurographics Association, 2008) Andrews, Bill; Bruckner, Stefan; Chen, Wei; Correa, Carlos D.; Ebert, David S.; Sousa, Mario Costa; Viola, Ivan; Maria Roussou and Jason Leigh
The area of illustrative visualization is concerned with developing methods to enhance the depiction of scientific data based on principles founded in traditional illustration. The illustration community has century-long experience in adapting their techniques to human perceptual needs in order to generate an effective depiction which conveys the desired message. Thus, their methods can provide us with important insights into visualization problems. In this tutorial, the concepts in illustrative visualization are reviewed. An important aspect here is interaction: while traditional illustrations are commonly only presented as static images, computer-assisted visualization enables interactive exploration and manipulation of complex scientific data. Only by coupling illustrative visualization with effective interaction techniques its full potential can be exploited. The tutorial starts with a detailed description of the entire traditional medical illustration production pipeline (techniques, tools, etc.) describing limitations and specific features to be researched and developed for more advanced tools. We then proceed discussing the importance and power of abstraction and interface issues in illustrative visualization. We present different ways of achieving abstraction in interactive settings discussing flexible representations for representing artistic visual styles. Next, we introduce the importance of intuitive interaction for illustrative visualization describing sketch-based approaches as an intuitive way of manipulating and exploring volumetric datasets. In the last part of the tutorial we present techniques for deforming volumes in various ways inspired by traditional illustration techniques such as the depiction of surgical procedures. We also describe how to deform and render in an illustrative fashion using by-example approaches.
Surface Reconstruction From Non-parallel Curve Networks
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Liu, L.; Bajaj, C.; Deasy, J. O.; Low, D. A.; Ju, T.
Building surfaces from cross-section curves has wide applications including bio-medical modeling. Previous work in this area has mostly focused on connecting simple closed curves on parallel cross-sections. Here we consider the more general problem where input data may lie on non-parallel cross-sections and consist of curve networks that represent the segmentation of the underlying object by different material or tissue types (e.g., skin, muscle, bone, etc.) on each cross-section. The desired output is a surface network that models both the exterior surface and the internal partitioning of the object. We introduce an algorithm that is capable of handling curve networks of arbitrary shape and topology on cross-section planes with arbitrary orientations. Our algorithm is simple to implement and is guaranteed to produce a closed surface network that interpolates the curve network on each cross-section. Our method is demonstrated on both synthetic and bio-medical examples.
Sketching and Composing Widgets for 3D Manipulation
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Schmidt, Ryan; Singh, Karan; Balakrishnan, Ravin
We present an interface for 3D object manipulation in which standard transformation tools are replaced with transient 3D widgets invoked by sketching context-dependent strokes. The widgets are automatically aligned to axes and planes determined by the user s stroke. Sketched pivot-points further expand the interaction vocabulary. Using gestural commands, these basic elements can be assembled into dynamic, user-constructed 3D transformation systems. We supplement precise widget interaction with techniques for coarse object positioning and snapping. Our approach, which is implemented within a broader sketch-based modeling system, also integrates an underlying widget history to enable the fluid transfer of widgets between objects. An evaluation indicates that users familiar with 3D manipulation concepts can be taught how to efficiently use our system in under an hour.
Curvature-Domain Shape Processing
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Eigensatz, Michael; Sumner, Robert W.; Pauly, Mark
We propose a framework for 3D geometry processing that provides direct access to surface curvature to facilitate advanced shape editing, filtering, and synthesis algorithms. The central idea is to map a given surface to the curvature domain by evaluating its principle curvatures, apply filtering and editing operations to the curvature distribution, and reconstruct the resulting surface using an optimization approach. Our system allows the user to prescribe arbitrary principle curvature values anywhere on the surface. The optimization solves a nonlinear least-squares problem to find the surface that best matches the desired target curvatures while preserving important properties of the original shape. We demonstrate the effectiveness of this processing metaphor with several applications, including anisotropic smoothing, feature enhancement, and multi-scale curvature editing.
Rendering Method for Flat Origami
(The Eurographics Association, 2008) Mitani, Jun; Katerina Mania and Eric Reinhard
In flat Origami (Origami which is folded flat), some cases exist that have a closed-loop in the overlap order of faces after they are folded. It is difficult to display this shape correctly on the screen when Origami is expressed by sets of plane polygons of zero thickness as is generally used in CG because all faces are placed on the same plane. In the present paper, we propose a new rendering technique to solve this problem. In the proposed method, we prepare a matrix that represents the overlap relation between two faces and a face ID buffer, the concept of which is similar to a Z buffer in the z-buffer algorithm. With this buffer, the face located in the uppermost is monitored in each pixel at the rendering stage. We render the shape on the face ID buffer using a scanline algorithm and display the folded shape by outputting the result in which the edges are extracted. Moreover, we render the shape in technical illustration style by coloring each vertex according to the number of mountain and valley folds connected to the vertex. In addition, we propose a simple pseudo shading algorithm.
Detail-In-Context Visualization for Satellite Imagery
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Boettger, Joachim; Preiser, Martin; Balzer, Michael; Deussen, Oliver
We use the complex logarithm as a transformation for the visualization and navigation of highly complex satellite and aerial imagery. The resulting depictions show details and context with greatly different scales in one seamless image while avoiding local distortions. We motivate our approach by showing its relations to the ordinary perspective views and classical map projections. We discuss how to organize and process the huge amount of imagery in realtime using modern graphics hardware with an extended clipmapping technique. Finally, we provide details and experiences concerning the interpretation of and interaction with the resulting representations.
From a Light CG Framework to a strong Cannibal Experience
(The Eurographics Association, 2008) Boers, Jerke; Dobbe, Jeroen; Huijser, Remco; Bidarra, Rafael; Steve Cunningham and Lars Kjelldahl
Game development courses are being more and more deployed within computer graphics (CG) curricula. A fundamental element in the pedagogical effectiveness of such courses is the quality of the development framework provided to the students. We discuss the most important challenges faced throughout the years while using, configuring and improving the framework for our games project, and describe the solutions we came up with to resolve those issues. We conclude that a carefully designed development framework, including all underlying technology, course material and quality support, significantly determine the quality of a project-based game development course. In addition, when the teams in such projects have an interdisciplinary character, providing an effective collaboration environment is crucial for the success of team members. We believe that the key to the huge success of our games project lies, to a great extent, in the deployment of a professional working environment specifically crafted for an educational setting.
Articulated Object Reconstruction and Markerless Motion Capture from Depth Video
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Pekelny, Yuri; Gotsman, Craig
We present an algorithm for acquiring the 3D surface geometry and motion of a dynamic piecewise-rigid object using a single depth video camera. The algorithm identifies and tracks the rigid components in each frame, while accumulating the geometric information acquired over time, possibly from different viewpoints. The algorithm also reconstructs the dynamic skeleton of the object, thus can be used for markerless motion capture. The acquired model can then be animated to novel poses. We show the results of the algorithm applied to synthetic and real depth video.
Image-based Shaving
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Nguyen, Minh Hoai; Lalonde, Jean-Francois; Efros, Alexei A.; De la Torre, Fernando
Many categories of objects, such as human faces, can be naturally viewed as a composition of several different layers. For example, a bearded face with glasses can be decomposed into three layers: a layer for glasses, a layer for the beard and a layer for other permanent facial features. While modeling such a face with a linear subspace model could be very difficult, layer separation allows for easy modeling and modification of some certain structures while leaving others unchanged. In this paper, we present a method for automatic layer extraction and its applications to face synthesis and editing. Layers are automatically extracted by utilizing the differences between subspaces and modeled separately. We show that our method can be used for tasks such beard removal (virtual shaving), beard synthesis, and beard transfer, among others.
Contact Skinning
(The Eurographics Association, 2008) Duriez, Christian; Courtecuisse, Hadrien; Alcalde, Juan-Pablo de la Plata; Bensoussan, Pierre-Jean; Katerina Mania and Eric Reinhard
In this paper, we propose a new approach to model interactions through a skinning method. Skinning is a frequently used technique to animate a mesh based on skeleton motion. In the case of a hand motion sequence used to manipulate and grasp virtual objects, it is essential to accurately represent the contact between the virtual objects and the animated hand. To improve the level of realism, our approach allows to accurately solve friction contact laws. In addition, contact constraints defined on the surface of the hand can be applied onto the skeleton to produce plausible motion. We illustrate our work through two examples: the real-time simulation of a grasping task and a character animation based on motion capture.
FMDistance: A Fast and Effective Distance Function for Motion Capture Data
(The Eurographics Association, 2008) Onuma, Kensuke; Faloutsos, Christos; Hodgins, Jessica K.; Katerina Mania and Eric Reinhard
Given several motion capture sequences, of similar (but not identical) length, what is a good distance function? We want to find similar sequences, to spot outliers, to create clusters, and to visualize the (large) set of motion capture sequences at our disposal. We propose a set of new features for motion capture sequences. We experiment with numerous variations (112 feature-sets in total, using variations of weights, logarithms, dimensionality reduction), and we show that the appropriate combination leads to near-perfect classification on a database of 226 actions with twelve different categories, and it enables visualization of the whole database as well as outlier detection.
Shadowed Relighting of Dynamic Geometry with 1D BRDFs
(The Eurographics Association, 2008) Nowrouzezahrai, Derek; Kalogerakis, Evangelos; Simari, Patricio; Fiume, Eugene; Katerina Mania and Eric Reinhard
We present a method for synthesizing the dynamic self-occlusion of an articulating character in real-time (> 170Hz) while incorporating reflection effects from 1D BRDFs under dynamic lighting and view conditions. We introduce and derive a general operator form for convolving spherical harmonics (SH) occlusion vectors with arbitrary 1D BRDF kernels. This operator, coupled with a compact linear model for predicting SH occlusion over articulating meshes, segments the BRDF and visibility terms of the direct illumination integral. We illustrate our results on a thin-membrane translucency model and the normalized Phong BRDF.
High-Resolution Volumetric Computation of Offset Surfaces with Feature Preservation
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Pavic, Darko; Kobbelt, Leif
We present a new algorithm for the efficient and reliable generation of offset surfaces for polygonal meshes. The algorithm is robust with respect to degenerate configurations and computes (self-)intersection free offsets that do not miss small and thin components. The results are correct within a prescribed ?-tolerance. This is achieved by using a volumetric approach where the offset surface is defined as the union of a set of spheres, cylinders, and prisms instead of surface-based approaches that generally construct an offset surface by shifting the input mesh in normal direction. Since we are using the unsigned distance field, we can handle any type of topological inconsistencies including non-manifold configurations and degenerate triangles. A simple but effective mesh operation allows us to detect and include sharp features (shocks) into the output mesh and to preserve them during post-processing (decimation and smoothing). We discretize the distance function by an efficient multi-level scheme on an adaptive octree data structure. The problem of limited voxel resolutions inherent to every volumetric approach is avoided by breaking the bounding volume into smaller tiles and processing them independently. This allows for almost arbitrarily high voxel resolutions on a commodity PC while keeping the output mesh complexity low. The quality and performance of our algorithm is demonstrated for a number of challenging examples.
Quadruped Animation
(The Eurographics Association, 2008) Skrba, Ljiljana; Reveret, Lionel; Hetroy, Franck; Cani, Marie-Paule; O'Sullivan, Carol; Theoharis Theoharis and Philip Dutre
Films like Shrek, Madagascar, The Chronicles of Narnia and Charlotte s web all have something in common: realistic quadruped animations. While the animation of animals has been popular for a long time, the technical challenges associated with creating highly realistic, computer generated creatures have been receiving increasing attention recently. The entertainment, education and medical industries have increased the demand for simulation of realistic animals in the computer graphics area. In order to achieve this, several challenges need to be overcome: gathering and processing data that embodies the natural motion of an animal which is made more difficult by the fact that most animals cannot be easily motion-captured; build accurate kinematic models for animals, in particular with adapted animation skeletons; and develop either kinematic or physically-based animation methods, either embedding some a priori knowledge about the way that quadrupeds locomote and/or building on some example of real motion. In this state of the art report, we present an overview of the common techniques used to date for realistic quadruped animation. This includes an outline of the various ways that realistic quadruped motion can be achieved, through video-based acquisition, physics based models, inverse kinematics, or some combination of the above. The research presented represents a cross fertilisation of vision, graphics and interaction methods.
Frontmatter
(The Eurographics Association and Blackwell Publishing Ltd, 2008)
Real-Time Rendering and Editing of Vector-based Terrains
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Bruneton, Eric; Neyret, Fabrice
We present a method to populate very large terrains with very detailed features such as roads, rivers, lakes and fields. These features can be interactively edited, and the landscape can be explored in real time at any altitude from flight view to car view. We use vector descriptions of linear and areal features, with associated shaders to specify their appearance (terrain color and material), their footprint (effect on terrain shape), and their associated objects (bridges, hedges, etc.).In order to encompass both very large terrains and very fine details we rely on a view dependent quadtree refinement scheme. New quads are generated when needed and cached on the GPU. For each quad we produce on the GPU an appearance texture, a footprint texture, and some object meshes, based on the features vector description and their associated shaders. Adaptive refinement, procedural vector features and a mipmap pyramid provide three LOD mechanisms for small, medium and large scale quads. Our results and attached video show high performance with high visual quality.
Designing Multi-projector VR Systems: from Bits to Bolts
(The Eurographics Association, 2008) Soares, Luciano Pereira; Dias, Miguel Salles; Jorge, Joaquim Armando Pires; Raposo, Alberto; Araújo, Bruno Rodrigues De; Bastos, Rafael; Maria Roussou and Jason Leigh
Immersive multi-projection environments are becoming affordable for many research centers, but these solutions need several integration steps to be fully operational; some of these steps are difficult and not in a common domain. This tutorial presents the most recent techniques involved in multi-projection solutions, from projection to computer cluster software. The hardware in these VR installations is a connection of projectors, screens, speakers, computers and tracking devices. The tutorial will introduce hardware options, explaining their advantages and disadvantages. We will cover software design and open source tools available, and how to administrate the whole solution, with tasks such as installing the computer cluster and configuring the graphical outputs. An introduction to tracking systems, explaining how electromagnetic and optical trackers work, will be also provided. At the end, we are going to present important design decisions in real cases: the project process, problems encountered, good and bad points in each decision.
What Can We Gain from Transdisciplinary Visualization Courses?
(The Eurographics Association, 2008) Chalmers, Panel Chair: Gitta Domik; Panellists: Alan; Domik, Gitta; Fellner, Dieter W.; Rushmeier, Holly; Steve Cunningham and Lars Kjelldahl
Transdisciplinary education means going even further in the collaboration with other disciplines than multidisciplinary and interdisciplinary education do. Transdisciplinary education attempts to search for new insights and views that emerge by balancing the importance of each participating discipline. Because most visualization problems are posted by disciplines other than Computer Science and because good solutions to visualization problems span knowledge over different disciplines, we often find interest from students outside the CS area in our visualization courses. This panel will discuss transdisciplinary (as well as interdisciplinary and multidisciplinary) visualization courses from four different viewpoints of the four panellists: What do multidisciplinary, interdisciplinary and transdisciplinary education mean in practical terms for an educator of a visualization course? What benefits does an applied research institute expect from graduates that have experience in interdisciplinary or transdisciplinary versus unidisciplinary collaboration? Will there be enough interest from non-CS students to attend such visualization courses?
Advanced Algorithms in Medical Computer Graphics
(The Eurographics Association, 2008) Klein, Jan; Bartz, Dirk; Friman, Ola; Hadwiger, Markus; Preim, Bernhard; Ritter, Felix; Vilanova, Anna; Zachmann, Gabriel; Theoharis Theoharis and Philip Dutre
Advanced algorithms and efficient visualization techniques are of major importance in intra-operative imaging and image-guided surgery. The surgical environment is characterized by a high information flow and fast decisions, requiring efficient and intuitive presentation of complex medical data and precision in the visualization results. Regions or organs that are classified as risk structures are in this context of particular interest. This paper summarizes advanced algorithms for medical visualization with special focus on risk structures such as tumors, vascular systems and white matter fiber tracts. Algorithms and techniques employed in intra-operative situations or virtual and mixed reality simulations are discussed. Finally, the prototyping and software development process of medical visualization algorithms is addressed.

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